These are links that can drive many thousands of visitors to your site, many of whom use these link lists to find blog material and places to link to, increasing their value exponentially to SEOs (this obviously relates directly to my last post on link bait). Recently, this comparison of Digg vs. Slashdot traffic caught my eye. I think it's a great case study and worthy of being scrutinized. Note what Kottke says:

I'm measuring (roughly) visitors from each of those sites. From the kottke.org data, you can infer how many people visit each site by how many people visited from each site initially...the bandwidth burst from Slashdot was roughly about 1.8 times as large as Digg's. That's actually almost exactly what Alexa shows (~1.8x).

But over a period of about 4 days, Slashdot has sent more than 4 times the number of visitors to kottke.org than Digg -- despite a 18-hour headstart for Digg -- and the aftershock for Slashdot is much larger and prolonged. It's been four days since the Slashdotting and kottke.org is still getting 15,000 more visitors a day than usual. This indicates that although Digg may rapidly be catching up to Slashdot traffic-wise, it has a way to go in terms of influence.

Does anyone know of comparable data on some of the others? I'd be thrilled to see what traffic looks like from Reddit and Yahoo! picks in particular.

One of my pages was recently linked to from an article featured on the NPR.org homepage. Thousands of visitors immediately and hundreds per day for a while afterwards.
The same page got about 1000 diggs last month and that resulted in a couple thousand links, mostly from blogs and scraper-type sites. But the NPR mention has already resulted in a couple of high quality links that will be worth far more than all of the blog and scraper links from the digg mention combined.